It has become accepted for certain medical indications to stabilize the relative position of vertebrae for at least some limited period of time. Anchor members are attached onto vertebral bodies, such as in the case of laminar hooks, or are implanted into the bodies using screw members. The anchors generally include means to hold a rod such as a clamping means which forms an integral part of the anchor. Adjacent anchors customarily hold respective vertebrae relative to a stabilizer, i.e. a plate or a rod.
In reciting the objectives of an assembly, it is critical to keep the biological context in mind. Thus, it is important not only to achieve the desired load limitations and stabilization characteristics, but also to design a series of components and respective instrumentation which is as easily manipulated and as quickly assembled as possible, which is as non-obtrusive into the biological environment as possible, and which is designed with the goal of avoiding failure. A surgeon may have limited physical access to the surgical site as well as obscured surgical visibility. It is critical to avoid the pieces or filings which could fall into a wound site. It is also important to design a system which can be manipulated by a gloved surgeon.
It is also desirable to have a system designed to allow as much flexibility for the surgeon as possible and yet to include some self-limiting features in order to maintain ease of application.
It is therefore an object of the current invention to provide a stabilizer anchor member having a closure means, which slides into position to capture an elongated stabilizer within the anchor member. The sliding closure means is designed to provide increased resistance to spreading of the anchor member.
It is a further object of the invention to provide a novel set screw which is self limiting and can achieve a higher torque. Moreover, the set screw allows for a gradual transition shear rather than a sudden snapping.
In addition, the set screw includes external prongs to mate with a removal instrument for removal of the set screw after shear.